The Solar Wind Observed by Ulysses

• But the solar wind is most directly observed in situ by a interplanetary spacecraft with plasma instruments to measure the wind's speed, elemental composition, ionization state, and the interplanetary magnetic field (IMF).

• Coordinated interplanetary and coronal observations have demonstrated that coronal holes are the source of wind streams with a much higher speed (>700 km/s) than the typical, slower (~400 km/s) wind.

• As first to fly far out of the ecliptic plane, the Ulysses spacecraft has measured steady high-speed wind from polar coronal holes.

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